EXCHANGE 


9061  '12 
*A  *M  ' 


•soig 


THE  UNIVERSITY  OF  CHICAGO 


The  Diffusion  of  Gases  and  the 
Density  of  Chlorine 

A  Search  for  Probable  Isotopes 
of  Chlorine 


A  DISSERTATION 

SUBMITTED  TO  THE  FACULTY  OF  THE  OGDEN  GRADUATE 

SCHOOL  OF  SCIENCE  IN  CANDIDACY  FOR  THE 

DEGREE  OF  DOCTOR  OF  PHILOSOPHY 


DEPARTMENT  OF  CHEMISTRY 


BY 
William  DeGarmo  Turner 


TABLE  OF  CONTENTS 


Outline I 

Introduction 2 

Historical 3 

The  Choice  of  a  Method 5 

Description  of  the  Apparatus   6 

Manipulation 7 

Corrections .  8 

Results   13 

Summary 14 


EXCHANGE 


THE  DIFFUSION  OF  GASES  AND  THE  DENSITY  OF  CHLORINE 

A  Search  for  Probable  Isotopes  of  Chlorine 

OUTLINE 

A  study  of  chlorine,  to  account  for  its  atomic  weight  of  35.46,  was 
made  through  the  medium  of  fractional  diffusion  as  a  means  of  separat- 
ing possible  isotopes.  To  investigate  the  method  and  determine  its  ap- 
plicability a  preliminary  investigation  was  made  with  the  gases  Methane 
(molecular  weight  about  16)  and  Ammonia  (molecular  weight  about 
17).  These  gases  proved  to  be  separable  by  means  of  a  diffusion  ap- 
paratus devised  for  the  occasion.  Moreover  a  diffusion  of  lead  nitrate 
in  water  solution  was  made  also,  to  study  this  type  of  diffusion  as  per- 
haps applicable  to  chlorine. 

The  method  of  gas  diffusion  was  chosen  and  a  system  designed  using 
as  a  diffusion  medium  clay  pipe  stems,  which  had  proved  to  be  the 
most  desirable  of  a  number  of  materials  considered.  The  chlorine  was 
subjected  to  fractional  diffusion  in  this  system  and  density  determina- 
tions were  made  on  both  the  end  fractions.  For  these  determinations  a 
number  of  density  bulbs  were  prepared  and  calibrated.  A  Balance  was 
specially  adjusted  for  the  weighings  and  was  enclosed  in  a  large  glass 
case  designed  to  protect  it  from  sudden  changes  of  temperature.  To 
determine  gas  pressures  accurately  a  precision  barometer  described  by 
A.  O.  F.  Germann,  was  constructed  and  this  also  was  enclosed  in  a  glass 
case.  For  final  density  determinations  two  volumeters  were  made  and 
to  purify  the  chlorine  for  these,  precipitated  gold  was  employed  in  a 
glass  tube  heated  by  a  specially  designed  electrical  unit 

Several  preliminary  results  were  obtained  all  serving  to  indicate  re- 
finements and  improvements  to  be  made  in  the  method  of  diffusion  and 
density  determination.  The  final  densities  after  the  equivalent  of  1,024 
fractionations  and  after  careful  purification  are  as  follows: 

I.  The  heavy  fraction  3.209  g.  per  1.  average. 

II.  The  light  fraction  3.203  g.  per  1.  average. 

These  results  indicate  that  chlorine  cannot  be  separated  into  its  iso- 
topes by  diffusion  of  chlorine  gas,  but  suggest  the  diffusion  of  Hydro- 
chloric Acid  gas  and  atomic  weight  determinations  by  analytical  methods. 


559 4 7G 


2  THE  DIFFUSION  OF  GASES  AND  THE  DENSITY  OF  CHLORINE 

INTRODUCTION 

Recent  studies  of  the  periodic  system  of  the  elements,  lt  2>  3  and  the 
more  perfect  formulation  of  the  relationships  between  the  atoms, 
especially  those  of  atomic  weight  below  59.0,  i.  e.,  the  first  twenty-seven 
elements,  have  led  to  the  recognition  of  certain  hitherto  unexplained 
peculiarities  of  certain  elements.  Among  these  is  chlorine  with  atomic 
weight  3546  and  in  a  study  of  its  atomic  weight  the  investigation  de- 
scribed in  the  following  pages  was  undertaken. 

It  has  been  shown2  that  for  the  elements  up  to  Cobalt  at  least,  the 
average  deviation  of  the  atomic  weight  from  whole  numbers  is  ex- 
tremely small  on  the  basis  of  oxygen  =  16,  and  of  these  first  twenty- 
three  elements  Magnesium  24.32  and  chlorine  35.46  are  the  only  ones 
which  show  large  departures. 

Again  the  determinations  of  the  weight  of  the  liter  normal,  of 
chlorine4  have  given  the  value  3.214  grams  per  liter  and  this  value 
leads  to  an  atomic  weight  of  35.28  much  lower  than  that  obtained  by 
chemical  or  physical  methods,  i.  e.,  35.46.  This  irregularity  also  has 
lead  to  many  attempts  at  an  explanation,  for  example,  by  assuming  a 
partial  dissociation  of  the  chlorine  at  ordinary  temperatures.  This  as- 
sumption however  has  been  shown  to  be  improbable  by  M.  Maurice 
Pellaton  in  a  careful  determination  of  the  physical  constants  of  chlorine5 
leading  to  the  conclusion  that  there  is  neither  dissociation  nor  associa- 
tion in  chlorine  gas.  Moreover,  E.  Marchand  has  determined  the  sur- 
face tension  of  liquid  chlorine  and  is  lead  to  the  conclusion  that 
chlorine  is  normal  in  the  liquid  state  also. 

It  has  been  recognized  in  recent  years  that  many  elements  exist  in 
isotopic  forms,  i.  e.,  that  one  element,  an  identity  chemically,  and  with 
a  single  atomic  number  and  so  far  as  is  known,  a  single  spectrum,  may 
arise  from  several  independent  sources  and  thus  consist  of  several  dif- 
ferent kinds  of  atoms  with  different  atomic  weights  or  indeed  with  the 
same  atomic  weight  and  different  intrinsic  internal  energies.  But  though 
these  isotopes  are  the  same  chemically,  they  may  differ  in  physical  prop- 
erties such  as  density  or  melting  point.  Thus  Richards6  has  shown  that 

1  Harkins  and  Wilson,  Proc.  Nat.  Acad.  Set.,  Vol.   I,  p.   276,   May,    1915. 

2  Harkins  and  Wilson,  /.  A.   C.  S.,  37,   1,367,  June,    1915. 

3  Harkins  and  Hall,  /.  A.    C.  S.,   38,    109,    Feb.,    1916. 

4  Jaquerod   and   Tourpaian,  /.    Chim.   Phyx.,   11,    3   and   269    (1913). 
,BM.    Maurice  Pellaton,  /.    Chim.   Phys.,   13,   426    (1915). 

6T.  W.  Richards,  7.  A.  C.  S.,  38,  221    (1916). 


THE:  DIFFUSION  OF  CASKS  AND  THE:  DENSITY  OF  CHI/DRINK  3 

lead  from  radium  has  a  different  density  from  ordinary  lead,  and  Soddy7 
has  shown  the  same  for  lead  from  thorium  and  ordinary  lead.  In  an 
entirely  different  type  of  investigation  (dependent  however  on  the  same 
physical  property,  density)  F.  W.  Aston  in  conjunction  with  Sir  J.  J. 
Thompson  has  attempted  the  separation  of  neon  by  fractional  diffusion, 
into  two  isotopes. 

In  the  light  of  all  these  considerations  it  seemed  probable  that  ordi- 
nary chlorine  must  be  a  mixture  of  isotopes  of  different  atomic  weight 
and  that  it  should  be  separable  into  its  constituent  parts  by  diffusion. 
Such  an  investigation  should  be  the  more  valuable  since  the  atomic 
weight  of  chlorine  is  so  fundamentally  important,  especially  as  the 
basis  of  other  atomic  weight  determinations. 

HISTORICAL 

Many  methods  have  been  used  for  the  study  of  gas  diffusions  but  few 
are  adapted  to  the  separation  of  gases  by  fractional  diffusions.  One  of  the 
early  workers  was  Loschmidt8  but  he  conducted  his  experiments  without 
the  use  of  porous  media  simply  diffusing  one  gas  directly  into  another. 
Later  Winkelmann9  and  Obermayer10  have  made  extended  investigations 
but  they  studied  the  speed  of  diffusion  in  long  narrow  tubes.  J. 
Stephan11  also  one  of  the  early  investigators  followed  Loschmidt  in  sim- 
ilar work.  More  recently  Ramsay  and  Rayleigh12  have  used  a  porous 
clay  pipe  for  fractional  diffusion  of  atmospheric  nitrogen,  and  Ramsay 
and  Collie13  and  Ramsay  and  Travers14  have  applied  the  same  methods 
to  clevite  gas.  Their  system  was  to  allow  the  gas  mixture  to  diffuse 
from  approximately  atmospheric  pressure  into  a  vacuum  so  that  there 
probably  was  an  effect  due  to  effusion  as  well  as  the  diffusion  effect. 
Since  pure  effusion  does  not  aid  in  the  separation  of  gases,15  an  ap- 
paratus designed  to  make  use  of  the  diffusion  only  would  ^eem  to  have 
some  advantages  over  other  types. 

7  Frederic    Soddy,   "The   Chemistry  of  the  Radio   Elements,"   II.    28. 

8  Loschmidt,    Wien.  Ber.,   61,    (2),   367    (1870);    Wlen.   Ber.,   62,    (2),   468    (1870). 
9Winkelmann,    Wied.  Ann.,   22,    i,    152    (1884);    Wied.  Ann.,   23,   203    (1884);    Wied.   Ann., 

26,  105  (1886);  Wied.  Ann.,  33,  445  (1888);  Wied.  Ann.,  36,  92  (1889);  Ann.  Phys.,  Q,  104 
(1901);  Ann.  Phys.,  8,  388  (1902). 

10  V.    Obermayer,    Wien.  Ber.,   81,    (2)    1,102;    Wien.  Ber.,  85,    (2)    147,   748    (1882);    Wien. 
Ber.,  96,   (2)   546. 

11  J.  Stephan,    Wien.  Ber.,  63,   (2)   63. 

12  Ramsay  and  Rayleigh,  Phil.  Trans.,   186,    187    (1895). 

13  Ramsay  and  Collie,  Proc.  Roy.  Soc.,  60,  206. 

14  Ramsay  and  Travers,  Proc.  Roy.  Soc.,  60,  206. 

15  M.  W.  Travers,  "The  Experimental  Study  of  Gases,"  p.  279. 


4  THE;  DIFFUSION  OF  GASES  AND  THE;  DENSITY  OF  CHLORINE 

Chlorine  has  been  the  basis  of  much  careful  study  particularly  from 
a  physical  standpoint,  since  it  offers  some  peculiarities  and  since  it  is  so 
abundant  and  fundamental  an  element. 

The  atomic  weight  of  chlorine  has  been  determined  by  many  investi- 
gators using  a  number  of  methods : — Dixon  and  Edgar,16  by  direct 
union  of  chlorine  with  Hydrogen,  Edgar17  alone  by  the  same  reaction 
chlorine  and  Hydrogen  but  different  procedure,  Noyes  and  Weber18 
also  by  direct  union  of  Hydrogen  and  chlorine,  Guye  and  Fluss19  by 
evolution  of  chlorine  from  nitrosyl-chloride,  Guye  and  TerGarzarian20 
by  density  and  critical  constants  of  Hydrochloric  Acid,  Gray  and 
Burt21  by  a  similar  physico-chemical  study  of  Hydrochloric  Acid,  Rich- 
ards by  production  of  Silver  Chloride  and  Ammonium  Chloride,  and 
Baume  and  Perrot22  determined  it  by  combining  Ammonia  gas  and 
Hydrochloric  gas.  These  methods,  all  either  chemical  or  dependent  first 
of  all  on  a  chemical  combination  lead  to  a  value  about  35.460. 

The  density  of  chlorine  has  been  determined  by  L,educ,23  Moissan  and 
Binet,24  and  Jaquerod  and  Tourpaian25  as  3.214  grams  per  liter  normal. 
This  will  give  35.28  as  the  atomic  weight  of  chlorine. 

Mention  has  been  made  of  the  work  of  Mr.  Pellaton26  one  of  the 
most  recent  works  on  chlorine  constants.  This  investigator  has  de- 
termined the  critical  temperature,  144°,  the  vapor  tension  of  liquid 
chlorine  from  100°  to  144°,  the  density  of  liquid  chlorine,  and  sat- 
urated vapor  at  7&9°  to  144°,  and  latent  heats  of  vaporization.  In  all 
of  these  determinations  the  chlorine  is  shown  to  obey  the  laws  for  nor- 
mal gases. 

The  surface  tension  of  liquid  chlorine  has  been  investigated  by  E. 
Marchand27  and  he  too  finds  it  to  be  a  normal  liquid. 

16  Dixon  and  Edgar,  Phil.  Trans.,  205,   169   (1905);  Dixon  and  Edgar,  Proc.  Roy.  Soc.,  A., 
76,  250  (1905). 

"Edgar,  Phil.  Trans.,  209,   i   (1908). 

18  Noyes  and  Weber,  7.  A.  C.  S.,  30,  13  (1908). 

19  Guye  and  Fluss,  7.   Chim.  Phys.,  6,  722   (1908). 

20  Guye  and  TerGarzarian,  C.  R.,  143,   1,233  (1906). 

21  Gray  and  Burt,  7.    C.  S.,   95,    1,633    (1909). 

22  Baume  and  Perrot,  Arch,  des  Sci.  phys.   and  Nat.,    (4),   32,   249    (1911);   Arch,   des  Set. 
phys.  and  Nat.,  (4),  34,  352   (1912);  7.  Chem.  Soc.,  II,   102,  933;   C.  R.,  155,  461    (1912). 

23Leduc,   C.  R.,   125,   571    (1897). 

24  Moissan  and   Binet,    C.   R.,   137,    1,198    (1903). 

25  Jaquerod  and  Tourpaian,  7.  Chim.  Phy.,  11,  3   (1913). 

26  M.   Maurice  Pellaton,  7.   Chim.  Phys.,  13,   426    (1915). 
2TE.  Marchand,  7.   Chim.  Phys.,  11,   573. 


THE;  DIFFUSION  OF  GASES  AND  THE  DENSITY  OF  CHLORINE  5 

THE  CHOICE  OF  A  METHOD 

The  method  to  be  chosen  for  separation  of  possible  isotopes  should 
depend  on  diffusion  since  the  speed  of  diffusion  of  gases  varies  with  the 
molecular  weights.  Furthermore  diffusion  has  been  attempted  in  such  a 
separation  in  the  case  of  neon  by  Aston,28  as  has  already  been  noted. 
Diffusion  of  a  salt  in  solution  might  also  effect,  a  separation  but  this 
method  is  less  rapid.  In  order  to  test  the  speed  of  separation  of  gases  of 
nearly  the  same  molecular  weights  investigation  was  conducted  on  the 
rate  of  separation  of  the  gases,  Methane  (atomic  weight  16)  and  Am- 
monia (atomic  weight  17).  The  rate  of  diffusion  of  a  lead  salt  in  aqueous 
solution  was  also  investigated.  The  results  of  these  investigations  showed 
that  gas  diffusion  is  moderately  rapid  since  a  mixture  of  approximately 
equal  volumes  of  Methane  and  Ammonia  may  be  diffused  by  a  process 
consuming  only  a  few  days  until  the  remaining  mixture  contains  about 
twelve  times  as  much  Ammonia  as  Methane.  On  the  other  hand  a  lead 
solution  after  more  than  a  year  had  diffused  upward  through  twenty-five 
centimeters  of  water  only  enough  to  give  a  negligible  concentration  at 
the  top. 

Accordingly  the  method  of  gas  diffusion  through  porous  material  was 
adopted.  In  principle  such  a  separation  might  be  conducted  after  a 
scheme  similar  to  that  used  in  fractional  crystallization  where  a  con- 
stantly increasing  number  of  simultaneous  separations  are  carried  on  by 
successive  combinations  of  each  light  with  its  neighboring  heavy  fraction. 
However  when  an  ample  supply  of  the  elementary  material  is  at  hand, 
the  intermediate  portions  may  be  discarded  and  only  the  end  fractions 
retained.  Now  in  a  separation  by  diffusion  the  heavier  constituent  will 
tend  to  remain  within  the  porous  tube  while  the  lighter  will  pass  through 
the  wall  in  excess.  The  gas  from  within  may  then  run  through  a 
second  tube,  what  passes  through  the  wall  may  be  discarded  as  an  inter- 
mediate fraction  and  what  remains  may  be  sent  through  a  third  and 
fourth,  <etc.  At  the  same  time  the  first  portion  which  has  come  from 
the  outside  may  be  sent  through  a  second  tube,  what  remains  within  may 
be  discarded  and  what  passes  through  the  wall  may  be  sent  through  a 
third  time,  etc.  Since  chlorine  could  be  obtained  in  abundance,  the 
second  type  of  separation  was  chosen  as  more  rapid  and  convenient. 

28  Aston,   Communication   to   British  Association   Meeting   (1913). 


6  THE  DIFFUSION  OF  GASES  AND  THE  DENSITY  OF  CHLORINE 

DESCRIPTION  OF  THE  APPARATUS 

The  apparatus  used  may  be  conveniently  described  under  four  heads : 
first,  that  for  purifying  the  chlorine ;  second,  the  diffusion  system ;  third, 
the  density  apparatus;  and  fourth,  the  accessories  such  as  balance,  ba- 
rometer, etc. 

The  chlorine  at  first  used  was  obtained  from  chemically  pure  Hydro- 
chloric acid  by  its  action  on  Potassium  permanganate,  but  this  method  of 
preparation  was  inadequate.  Later  it  was  found  necessary  to  repurify 
the  chlorine  after  passing  it  through  the  diffusion  train,  so  commercial 
electrolytic  chlorine  kindly  furnished  by  the  Electro  Bleaching  Gas  Co. 
of  Buffalo,  New  York,  was  employed.  This  was  passed  through* a  care- 
fully designed  purifying  train  of  copper  sulphate  solution,  sulphuric  acid 
and  phosphorus  pentoxide,  all  sealed  glass  to  glass,  thence  it  went  into 
the  diffusion  apparatus  and  the  fractions  were  passed  through  another 
similar  train  into  a  tube  containing  precipitated  gold  heated  to  about  200° 
C.  Here  it  was  absorbed  giving  auric  chloride,  and  this  tube,  after  the 
absorption,  could  be  heated  to  300°  C.,  reevolving  chlorine  which  was 
then  passed  through  two  phosphorus  pentoxide  tubes  and  thence  directly 
into  the  final  density  apparatus. 

The  diffusion  apparatus  consisted  of  two  systems  of  diffusion  tubes 
enclosed  in  separate  chambers.  The  porous  material  chosen  after  in- 
vestigation of  "Filtros,"  "Alundum,"  etc.,  was  ordinary  Scotch  clay 
pipe  stem.  These  were  selected  because  they  were  dense  and  fairly  thick- 
walled,  thus  preventing  too  rapid  a  diffusion  or  effusion. 

The  first  system  was  designed  to  collect  the  lighter  fraction  and  con- 
sisted of  a  single  stem  sealed  in  a  glass  jacket  similar  to  a  condenser 
jacket.  Through  this  jacket  a  current  of  pure,  dry  air  was  passed  into 
a  condenser  bulb  immersed  in  liquid  air  which  condensed  out  the  chlorine 
and  allowed  the  air  to  pass. 

The  second  system  received  the  discharge  from  the  pipe  stem  of  the 
first  system,  and  consisted  of  a  series  of  twenty  pipes,  or  about  forty 
feet. sealed  in  a  glass  box  through  which  a  current  of  pure,  dry  air 
was  passed  to  the  waste  line.  This  glass  box  was  provided  with  ma- 
nometer, pressure  regulator,  distribution  manifolds,  etc.,  to  insure 
proper  control  of  the  air  currents. 

The  chlorine  which  passed  out  of  the  pipes  of  this  system  was  con- 
ducted through  a  second  condenser  in  liquid  air  which  retained  the 


THE;  DIFFUSION  OF  GASES  AND  THE  DENSITY  OF  CHLORINE  .          7 

chlorine  and  allowed  the  air  which  had  diffused  into  it  to  escape.  From 
either  of  these  liquid  air  condensers  the  chlorine  could  be  transferred  by 
distillation  to  the  density  apparatus. 

The  density  apparatus  was  constructed  according  to  the  practice  of 
Germann,29  and  consisted  of  three  carefully  calibrated  bulbs  provided 
with  stop  cock  and  ground  glass  joint  for  attachment  to  the  chlorine 
train.  The  train  was  provided  with  adequate  apparatus  for  producing, 
measuring  and  controlling  a  vacuum  within  the  system.  The  bulbs  were 
calibrated  by  the  method  of  Germann,  observing  also  a  contraction  under 
vacuum  as  first  noticed  by  Rayleigh.30 

The  accessories  included  a  Sartorius  balance  for  calibrating  the  bulbs 
with  a  capacity  of  two  kilos  and  sensitive  to  one-tenth  milligram.  The 
balance  used  for  weighing  the  gas  was  a  long-armed  Troemner  rendered 
much  more  sensitive  and  convenient  by  suspending  small  trays  for  the 
weights  near  the  knife  edges.  This  balance  was  protected  from  sudden 
changes  in  temperature  by  surrounding  it  entirely  with  a  larger  glass  case 
which  provided  also  a  chamber  in  which  to  keep  the  glass  bulbs  before 
and  after  weighing.  The  weights  used  were  standardized  by  the  U.  S. 
Bureau  of  Standards  and  recalibrated  by  the  method  of  Richards.81 

For  reading  pressures  two  barometers  were  employed,  a  standard  brass 
scale  barometer  recently  calibrated  and  a  specially  constructed  barometer 
as  described  by  Germann,32  except  that  a  mirror  scale  was  used  in  place 
of  the  plate  glass  scale  as  described.  For  low  pressures  an  improved 
MacLeod  gauge  was  used. 

To  prevent  as  far  as  possible  any  photo  chemical  effect  the  entire 
train  of  diffusion  and  density  apparatus  was  painted  black  or  covered 
with  black  paper,  except  where  observations  had  to  be  made.  Stop 
cocks  and  ground  joints  were  lubricated  with  a  chlorinated  stop  cock 
grease  described  by  Wourtzel.33 

MANIPULATION 

Before  starting  the  diffusions  the  entire  system  was  swept  out  for  a 
week  with  pure,  dry  air,  then  for  two  days  with  pure  chlorine.  Chlorine 
was  then  allowed  to  stand  at  rest  in  the  apparatus  for  a  week,  during 

29  7.  Phys.,   19,  438    (1915). 

30  S.   Rayleigh,  Proc.   Roy.   Soc.,  43,   361    (1888). 
"Richards,  Zeit.  Phys.   Chem.,  33,  605    (1900). 

32  A.   O.   F.   Germann,  7.   A.   C.  S.,   36,  2,456   (1914). 

33  Wourtzel,  7.    Chim.  Phys.,   11,   29    (1913). 


8  THF,  DIFFUSION  OF  GASES  AND  THE  DENSITY  OF  CHLORINE 

which  time  only  the  slightest  visible  action  on  lubricating  grease,  seal- 
ing wax,  etc.,  could  be  observed.  The  apparatus  was  then  swept  out 
again  with  air  and  chlorine  was  then  passed  through  the  system  at  the 
rate  of  four  or  five  bubbles  per  second.  Meanwhile,  the  air  currents 
in  the  outer  jacket  wTere  passed  at  a  rate  about  six  times  as  fast.  At  the 
end  of  a  week  the  condensers  in  liquid  air  were  nearly  full  of  chlorine. 
The  heavier  fraction  was  then  passed  into  a  storage  bulb  in  liquid  air 
while  the  lighter  fraction  was  rediffused  through  the  apparatus.  Like- 
wise, the  heavier  fraction  was  also  rediffused.  These  operations  were 
repeated  eight  times  thus  giving  the  equivalent  of  128  fractionations. 
Upon  the  final  fractions  density  determ*  nations  were  then  made. 

It  was  decided  after  a  survey  of  the  first  series  of  diffusions  that 
the  lighter  fraction  was  too  small  and  to  remedy  this  condition  the  first 
section  of  the  diffusion  apparatus  was  made  about  three  times  as  long. 
With  this  addition  a  diffusion  run  required  about  two  days  instead  of  a 
week,  and  as  before  a  series  of  eight  runs  was  made,  the  densities  of  the 
two  final  fractions  were  determined,  and  these  fractions  were  added  to 
the  first.  These  final  combined  fractions  were  then  each  rediffused 
three  times,  giving  the  equivalent  of  1,024  individual  operations.  On 
these  final  end  fractions  density  determinations  were  made  employing 
every  possible  refinement  in  the  manipulation. 

CORRECTIONS 

Throughout  the  work  a  number  of  corrections  had  to  be  introduced. 
The  experimental  data  necessary  to  make  them  have  already  been  de- 
scribed. The  methods  of  applying  them  may  now  be  considered  under 
four  heads: — 

A.  Corrections  for  barometer  readings, 

B.  For  calibration  of  density  bulbs, 

C.  '  For  weight  of  density  bulbs, 

D.  For  weight  of  ampoules. 

A.     Considering  first  the  barometer  readings. 

i.     The  first  correction  to  be  applied  is  that  for  the  meniscus.     This 

is  an  additive  correction  and  is  given  by  the  formula  C  ( ) 

\Ru      SU/ 

in  which  C  is  a  constant  6.6  for  mercury.  Ru  and  R1  are  the  radii  of 
curvature  of  the  upper  and  lower  meniscii,  respectively.  Since  the  di- 
ameter of  the  tube  was  25  millimeters  in  the  glass  scale  barometer  the 


THE:  DIFFUSION  OF  GASDS  AND  THE  DENSITY  OF  CHLORINE;  9 

meniscus  becomes  almost  flat  and  Ru    and  R,      are  very  large.     This 

makes    —    and  —       very  small  and  since  they  are  approximately  equal 
Ru  RI 

their  difference  is  extremely  minute  and  may  be  altogether  neglected. 
The  diameter  of  the  lower  cup  in  the  brass  scale  barometer  was  about 
six  centimeters  so  its  curvature  was  zero,  the  diameter  of  the  upper 
tube  was  about  fifteen  millimeters  and  the  average  height  of  the  men- 
iscus about  fifteen  hundredths  of  a  millimeter,  and  its  radius  of  curva- 
ture becomes  therefore  about  fifty-five  millimeters  with  a  positive  cor- 
rection therefore  of  [6.6  ( )  =  0.120  millimeter].  The  varia- 

\55        o7 

tion  of  the  height  of  the  meniscus  from  reading  to  reading  was  slight, 
and  so  a  consistent  value  of  twelve  hundredths  of  a  millimeter  was 
added  to  each  reading. 

2.  The  second  correction  was  for  temperature.     Accurate  thermomr 
eters  were  hung  at  top  and  bottom  of  the  barometer.     These  usually 
read  the  same  degree  but  if  any  difference  was  noted  the  mean  of  the 
two  was  taken  and  the  correction  for  th's  temperature  was  taken  from 
the   standard  tables   for  glass   and  brass   scale   given   in   "Landolt   and 
Bornstein,  Tabellen." 

3.  The  third  correction  was  applied  only  to  the  glass  scale  and  was 
for  the  calibration  of  this  scale  against  a  standard  brass  meter  from  the 
Societe  Genevoise.     A  calibration  curve  was  made  plotting  every  cen- 
timeter but  as  the  variation  was  never  more  than  one-hundredth  of  a 
millimeter  from  a  stra:ght  line  function,  only  the  linear  correction  was 
made.     This  was  -{-0.022  millimeter  per  meter  at  zero  degrees  or  0.017 
millimeter  in  the  neighborhood  of   seventy-five  centimeters.     This  was 
rounded  off  to  0.02  millimeter  and  was  added  after  the  correction  to 
zero  degrees  had  been  made. 

4.  The  last   correction   was   for  location,   i.   e.,   a  correction  of  the 
weight  of  the  mercury,  to  45°   N.   latitude  and   sea  level.      Since  the 
latitude  of  Chicago  is  41°  50'  and  height  above  sea  level  is  175  meters 
these  corrections  may  be  taken  directly  from  The  Smithsonian  Meteoro- 
logical Tables,  and  for  barometer  readings  between  740  and  760  mil- 
limeters will  be : 

For  sea  level  correction  — 0.03  millimeter. 

For  45°  N.  latitude  correction         — 0.21  millimeter. 


).24  millimeter. 


IO  THE  DIFFUSION  OF  GASES  AND  THE  DENSITY  OF  CHLORINE 

This  correction  was  subtracted  from  each  reading  after  the  other  cor- 
rections had  been  applied. 

The   final    formula   then   for   barometer   readings   was    for   the   glass 
scale — 

H  ==  Ho  —  T  +  o.02  —  0.24  =  Ho   --T  —  0.22. 
and  for  the  brass  scale — 

H  =:  Ho  +0.12  —  T  —  0.24  =  Ho   --T  —  0.12. 

B.     Considering  next  the  corrections  for  the  calibration  of  the  den- 
sity bulbs. 

1.  The   first   correction   was    for   the   buoyancy   of   the   air   on   the 
weights  and  water.     Since  the  bulb  was  weighed,  both  filled  with  water 
and  empty,  with  its  counterpoise  which  experienced  the  same  buoyant 
effect  this  correction  became  zero.     The  effect  on  the  weights  however 

W 
amounted  to   -    -   x  d  where  W  is  the  weight  of  water,  8.5  the  density 

8-5 

of  brass  and  d  the  density  of  air  which  is  about  0.0012  grams  per  centi- 
meter. 

2.  The  second  correction  was  for  the  density  of  water  at  zero  degrees 
or  at  twenty  degrees  C.    Taking  the  density  of  water  at  zero  as  0.999841 
the  correction  to  be  added  is  0.000159  W,  or  taking  the  density  of  water 
at  twenty  degrees  as  0.998203  the  correction  to  be  added  is  0.001797  W. 

3.  The  correction  for  altitude  and  latitude34   35>  36  was  not  made  be- 
cause the  gas  was  referred  to  water  as  a  standard  by  the  method  of  de- 
termination employed.     When  the  density  of  a  gas  is  referred  to  that 
of  water,  then  if  the  density  of  water  is  given  in  terms  of  its  weight  at 
sea  level  and  45°   N.  lat.,  the  density  of  the  gas  will  also  be  so  ex- 
pressed without  further  correction.     Such  a  correction  is  made  by  Ger- 
mann  for  instance.34    In  his  case  the  density  of  water  is  taken  as  0.999868, 
a  value  which  is  referred  to  the  weight  of  water  at  four  degrees  C.  as 
i.oooooo.37     The  correction  to  be  applied  for  location  should  therefore 
have  been  referred  to  the  altitude  and  latitude  of  that  place  where  water 
has  an  absolute  weight  of   i.oooooo  grams  at   four  degrees  C.     If  in- 
stead of  0.999868,  the  absolute  density  of  water  had  been  taken,  i.  e.,  the 
density  expressed  in  terms  of  the  weight  of  one  centimeter  of  water  at 
zero  degrees  C  at  forty-five  degrees  N.  latitude  and  sea  level,  then  no 
correction  would  have  been  necessary. 

84  Germann,  7.  Phys.   Chem.,   19,  472    (1915). 
35  Guye,  7.   Chim.  Phys.,  5,  203    (1907). 

86  Gray  and  Burt,  7.    Chem.   Soc.,  95,    1,636    (1909). 

87  Thiesen,    Wiss.   Abh.   Phys.-Tech.   Reich,   3,   68    (1900). 


THE  DIFFUSION  OF  CASKS  AND  THE  DENSITY  OF  CHLORINE  II 

This  correction  may  be  considered  further.  The  reductions  to  forty- 
five  degrees  N.  latitude  and  sea  level,  of  weighings  made  by  counter- 
balancing with  a  set  of  standardized  weights  should  be  dependent  upon 
the  way  in  which  the  set  has  been  standardized.  If  it  has  been  checked 
against  weights  which  are  correct  at  forty-five  degrees  N.  latitude  and 
sea  level,  then  it  will  give  results  wherever  it  is  used  which  are  also 
standard  at  forty-five  degrees  N.  latitude  and  sea  level,  for  whatever 
mass  will  counterbalance  a  given  weight  in  one  location  will  counter- 
balance the  same  piece  in  any  other  location.  Furthermore,  if  the  set 
has  been  checked  against  weights  standard  at  some  location  other  than 
forty-five  degrees  N.  latitude  and  sea  level,  then  that  location  is  the  one 
to  use  in  making  corrections  to  absolute  weight,  and  not  the  location  in 
which  the  set  happens  to  be  used. 

The  same  reasoning  applies  to  weights  of  gas  which  are  referred  to 
corresponding  weights  of  water.  If  the  water  weight  is  correct  at  sea 
level,  etc.,  i.  e.,  if  its  absolute  density  is  taken,  then  the  absolute  density 
of  the  gas  is  given  without  correction.  For  example,  suppose  a  gas  is 
weighed  in  a  given  flask  in  some  location,  and  suppose  the  flask  is  cali- 
brated with  water  using  the  same  set  of  weights,  which  need  not  be 
standard  but  must  be  relatively  correct.38  Call  the  weight  of  gas  at 
zero  degrees  C.  for  simplicity  A,  and  the  weight  of  the  water  in  the 
same  volume  at  zero  degrees  C.  800  A.  Then  at  zero  degrees  C.  the 

gas  weighs  as  much  as  water  in  the  given  location.     It  will  also 

weigh    —       .  as  much  at   forty-five  degrees  N.   latitude  and   sea  level 

oOO 

and  if  absolute  density  of  water  is  used  in  the  calculation  then  absolute 
density  of  the  gas  will  be  given  directly.  Furthermore  if  absolute  den- 
sity has  not  been  used  the  necessary  correction  to  sea  level  will  be  de- 
pendent only  on  the  value  of  density  which  has  been  accepted  and  will 
be  independent  of  the  location  in  which  the  investigation  is  made  and  of 
the  particular  weight-pieces  used. 

C.  Considering  next  the  corrections  for  the  weight  of  the  density 
bulbs  of  chlorine. 

i.  The  first  correction  is  for  buoyancy  of  the  air  on  the  weights  used. 
Since  the  bulb  is  counterpoised,  the  only  correction  is  for  the  change  in 

W 
weights  and  is  given  by,    - —  x  0.00120  where  W  is  the  weight  used, 

*5 
the  0.00120  is  the  density  of  air  and  8.5  is  the  density  of  brass.    This  cor- 

38  Gray  and  Burt,  7.   Chem.  Soc.,  95,    1,636   (1909). 


12  THE  DIFFUSION  OF  GASES  AND  THE  DENSITY  OF  CHLORINE 

rection  applies  to  all  weights  whether  of  brass  or  not,  since  they  were  all 
calibrated  against  a  brass  standard.39  This  must  be  subtracted  since  the 
actual  weight  added  to  replace  the  chlorine  is  less  by  this  amount  than 
the  face  value  of  the  weights. 

2.  The  second  correction  is  for  the  contraction  of  the  bulb  on  evacua- 
tion.   This  is  equal  to  the  weight  of  air  displaced  when  the  bulb  expands 
and  is  therefore  given  by  S  x  0.00120  where  S  is  the  change  in  volume. 
This  must  be  added  to  the  weight  since  the  bulb  in  buoyed  up  by  less 
air  and  therefore  weighs  too  heavy  when  evacuated. 

3.  The  third  correction  is  for  the  residual  chlorine.     This  may  be 

computed  as  a  pressure  by  means  of  the  formula — = —  x  P  and  applied 

as  a  correction  to  be  subtracted  from  the  pressure  of  the  chlorine 
or  it  may  be  computed  in  weight  by  means  of  the  formula  0.003214  x 

27  T>  P 

'       x  — - —  x  V  and  added  to  the  weight  of  the  chlorine.     Since  it 
1  700 

varied  somewhat  from  time  to  time  it  was  found  convenient  to  com- 
pute it  as  a  pressure  thus  avoiding  a  separate  computation  for  each  in- 
dividual bulb. 

4.  The  fourth  correction  is  for  the  compressibility  of  the  chlorine, 
that  is  for  its  deviation  from  a  normal  gas  within  the  range  of  the  pres- 
sure change  involved  in  the  computation  of  the  weight  of  the  liter  nor- 
mal.    This  pressure  change  was  never  great,   from  760  to  about  745 
usually,  but  might  be  applied  either  in  the  computation  of  the  true  volume 
or  as  an  additive  correction  after  the  computation  was  made. 

D.  Only  one  correction  was  applied  to  the  weight  of  the  ampoule. 
This  was  for  the  buoyancy  of  the  air,  and  since  the  ampoule  was  weighed 
without  counterpoise  the  correction  was  applied  both  to  the  weights  and 
to  the  ampoule.  The  correction  may  be  represented  by  the  formula 
—  W  •=  Wo  +  S(Vs  •  -  Vw  ).  Where  W  is  correct  weight,  Wo  ob- 
served weight,  d  density  of  air,  Vs  and  V  w  the  volume  of  the  sub- 
stance and  of  the  weights,  now  V  —  -  —  for  brass  calibrated  weights 

8-5 

and  V  may  be  computed  from  the  weight  of  the  ampoule  in  air  (Wa  ) 
and  in  water  (Ww  )  by  the  formula  -  -  Vf  =Wa  -  Ww  with  suf- 
ficient accuracy.  Then  using  the  average  value  for  d  as  0.00117,  the  for- 
mula reduces  to  -  -  W  =  1.001032  Wa —  0.00117  W  w.  This  cor- 
rection was  applied  both  to  the  full  and  empty  ampoule. 

39  Gray  and  Burt,  J.   Chem.  Soc.,  95,   1,636    (1909). 


THE  DIFFUSION  OF  CASKS  AND  THF,  DENSITY  OF  CHLORINE 

RESULTS 
Results  of  all  Determinations  are  Tabulated  Below : 


TABLE  I. — CALIBRATION  OF  BULBS. 


Bulb  Mo. 

Weight  of 
water,  first 

Weight  of 
water,  second 

Volume 
first 

Volume 
second 

I 
II 
III 

IV 

310.549 
677.906 
889.570 
678.173 

310.529 

889.554 
678.137 

310.556 
677.920 
889.587 
678.186 

310.536 

889.571 
678.150 

TABLE  II — CONTRACTION  BY  METHED  OF  RAYLEIGH 

Bulb  No.  I  II  III 


IV 


Volume 

310.546               677-920               889.579 

678.168 

Contraction                 0.0025                  0.0105 

0.006O 

0.0005 

TABLE 

III.—  DENSITY 

AFTER  FIRST 

SERIES. 

Bulb 

Corrected 
barometer 

Corrected 
weight 

Corrected 
weight 

True  weight 
of 

Weight 
per  liter 

millimeter 

evacuated 

full 

chlorine 

normal 

I     a 

752.51 

1.8906 

0.9040 

0.9864 

3.208 

b 

752.51 

2.6926 

0.5530 

2.1393 

3.187 

II     a 

748.11 

1.8901 

0-9337 

0.9562 

3-201 

b 

748.11 

2.6922 

0.5469 

2.1450 

3-214 

c 

748.11 

34913 

0.6807 

2.8  IO2 

3-209 

TABLE 

IV.  —  DENSITY 

AFTER  SECOND 

SERIES. 

Bulb 

Corrected 
barometer 

Corrected 
weight 

Corrected          True  weight 
weight                      of 

Weight  per 
liter 

millimeter 

evacuated 

full 

chlorine 

normal 

I     a 

746.74 

1.8904 

0.9147 

0-9755 

3-197 

b 

746.74 

34918 

0.6864 

2.805O 

3-209 

II     a 

746.34 

1.0960 

0.9321 

0.9742 

3-195 

b 

746.34 

2.6973 

0.5627 

2.1350 

3.206 

c 

746.34 

3.5025 

0.7054 

2.7975 

3.202 

TABLE  V.—  DENSITY  AFTER  COMBINED  SERIES,  REFINED  APPARATUS 
HEAVY  FRACTION  ONLY. 


Bulb 

Corrected 
barometer 
millimeter 

Corrected 
weight 
evacuated 

Corrected 
weight 
full 

True  weight 
of 
chlorine 

Weight  per 
liter 
normal 

I 
II 
III 

746.09 
746.09 
746.09 

1.8912 
2.6930 
3-4920 

0.9129 
0.5561 
0.6908 

0.9781 
2.1366 
2.8008 

3.2084 
3.2092 
3.2072 

14  THE  DIFFUSION  OF  GASES  AND  THE  DENSITY  OF  CHLORINE 

TABLE  VI. — DENSITY  AFTER  COMBINED  SERIES,  REFINED  APPARATUS, 
LIGHT  FRACTION  ONLY. 


Ampoule 

Corrected 
volume  of 
apparatus 

Corrected 
weight  of 
ampoule 
full 

Corrected 
weight  of 
ampoule 
empty 

Corrected 
barometric 
pressure 

Weight  per 
liter 
normal 

I 
II 

1408.779 
1423-731 

23.8677 
23.0346 

19-4477 
18.5730 

742.49 
742.00 

3-2019 
3.2037 

The  above  results  may  be  summarized  showing  the  heavy  fraction  to 
average  3.208  grams  per  liter,  and  the  light  fraction  to  average  3.203 
grams  per  liter.  The  conclusion  to  be  drawn  from  these  results  is  that 
chlorine  as  a  gas  cannot  be  separated  into  its  isotopes  by  diffusion.  This 
is  probably  due  to  the  fact  that  the  gas  molecules  in  chlorine  consist  of 
combinations  of  both  lighter  and  heavier  fractions,  as  well  as  combina- 
tions of  two  atoms  of  the  lighter  or  two  atoms  of  the  heavier.  A  further 
conclusion  may  be  drawn  that  density  determinations  involve  great  dif- 
ficulties in  manipulative  technique. 

A  preliminary  experiment  on  the  diffusion  of  methane  and  ammonia, 
however,  has  shown  the  reliability  and  ease  of  separating  two  gases  of 
slightly  different  density  by  diffusion.  A  continuation,  therefore,  of 
this  investigation  will  involve  the  fractional  diffusion  of  hydrochloric 
acid  gas  and  the  determination  of  the  weight  of  its  chlorine  content  by 
gravimetric  and  volumetric  analytical  methods. 

SUMMARY 

Since  the  atomic  weight  of  chlorine  shows  some  irregularity  when  con- 
sidered in  the  light  of  formulae  recently  developed  in  a  study  of  the 
periodic  system,  an  attempt  was  made  to  account  for  this  abnormality. 

The  chlorine  was  subjected  to  a  series  of  fractional  diffusions  in  a 
specially  designed  apparatus  and  the  density  of  the  end  fractions  was 
determined.  Preliminary  density  determinations  were  made  from  time 
to  time  with  a  refined  type  of  density  bulb  apparatus.  This  proved  in- 
sufficient for  the  final  determinations  and  for  these  a  special  volumeter 
without  stop  cocks  was  employed  after  taking  careful  precautions  to  in- 
sure a  pure  chlorine. 

The  results  indicate  that  chlorine  cannot  be  separated  into  its  isotopes 
by  diffusion  of  chlorine  gas,  and  that  density  determinations  are  too 
tedious  as  a  means  of  determining  atomic  weight.  An  investigation  by 
diffusion  of  Hydrochloric  Acid  and  analytical  determination  of  atomic 
weights  has  since  been  carried  out  in  this  laboratory. 


5594 rc" 


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